Just a thought,are the screws catching on any wires at all,only other thing,maybe when you tighten them up,it pulls on a circuit board,i had the same sort of problem on a dvd remote,in the end theres was a transistor that was not soldered very well & its was just enough to stop it working,may not be your problem,i opened it up & tried with my finger to see if any parts moved & found it.
Goldman